Femtosecond-laser-induced refractive index modification has provided a flexible tool to fabricate three-dimensional photonic devices. Magneto-optical (MO) glass is widely used in integrated optics because of its Faraday rotation. Femtosecond laser at 1 kHz repetion rate is used to write waveguides in MO glass, then near-field modes of waveguides written by different focusing parameters are measured, and the refractive index changes in the written regions and mode field diameters as functions of writing parameters (scanning speed and writing power) are obtained, which show a writing window of waveguide formation in MO glass. Experimental results show that the Verdet constant in the written region only has a slight reduction (about 2.8%) under a special writing parameter set (10×, objective scanning speed 40 μm/s, laser power 3 mW); the loss of the waveguide is 1.53 dB/cm, and its mode field diameter is 10 μm injected by 980 nm, so it is practicable to couple light from fiber into waveguide written by femtosecond laser.